Developing biomechanical models from initiated fall actions and reactions in frail elderly patients Our goal is to identify primary actions and reactions during an initiated fall (a near miss) and to explore the balance recovery strategies in frail elderly patients, during ingress and egress from a hospital bed and chair. Extensive prior research on balance and weight shifting in falls has been conducted in the laboratory with normal subjects, or by using video observational research conducted in nursing homes of mobile patients with moderate gait impairment. The potential to explore fall mechanisms with frail elderly patients with an extremely high risk of injury, makes our dataset significant, and the further exploration of these data, an urgent priority. Secondary analyses of this unique dataset of frail elderly during bed and chair ingress/egress in a hospital room (AHRQ #1R01HS018953) will provide data-driven insights into falls in frail patients with impaired gait and enable the development of innovative fall interventions. The objective in this application is to test the effectiveness of recovery strategies (stepping, reaching, adjustments of trunk and head). In these subjects, the biomechanical mechanisms differ and are less effective than those in healthier subjects: corrective reactive stepping is shorter; arm reach is less pronounced; grip force weaker; and response time slower. We will develop an innovative biomechanical research strategy for targeting the points at which the fall mechanisms are initiated and explore how balance recovery is achieved by the frail elderly. This secondary use of our comprehensive dataset of 88 frail elderly and controls (n=1442 trials), provides data comprised of 3D movement, ground reaction forces, physiological metrics, fall history and functional assessments. These data are ideal for resolving the ethical dilemma in fall research with frail elderly, i.e. the absence of an actual fall. Our data reveal moments of instability and corrective behaviors used by patients to prevent a fall, during weight and balance transfers. Strategies that have not been previously investigated, most notably bouncing-to-stand from bed or chair, appear to be critical for identifying moments of fall risk, and preventative strategies. This significant research will overcome critical barriers by increasing knowledge about the exact points at which falls likely occur, including bouncing vs not bouncing on sit-to-stand, and the effectiveness of recovery strategies during balance transfers in frail elderly. The significance of this research is twofold: 1) documenting the biomechanics of a fall in the frail elderly, the degree of imbalance and the limited effectiveness of recovery strategies, will lead to modifications of fall interventions; and, 2) for subsequent research, the jerk responses will serve as proxy indices for a fall in laboratory research.